Tropical Forest Phenology and Satellite Vegetation Index Validation

Abstract

Phenology, the study of life cycle events, is gaining importance globally as the onset of climate change is impacting the timing of forest and agriculture growth cycles. Phenological research often involves land surface phenology (LSP) analysis derived from satellite vegetation indices (VI's) such as those from Moderate Resolution Imaging Spectroradiometer (MODIS). Due to persistent cloud cover and atmospheric interference in tropical regions, satellite VI time series are subject to uncertainties and thus require near surface vegetation monitoring systems for ground-truthing. This study was designed to quantify the precision of MODIS phenological signatures using an above-canopy, down-looking digital camera installed on a flux tower in Hawaiʻi Volcanoes National Park. Though static seasonality was predicted, quantitative measures derived from in-situ camera images illustrated moderate fluctuation in canopy greenness that was not detected by MODIS. These results indicate the limitations of MODIS for tropical locations and emphasize the need for continued in-situ phenology research.